The costimulatory pathway consisting of the programmed death-1 (PD-1) receptor and its ligand, PD-L1 (or B7-H1 or CD274) is known to contribute directly to T cell exhaustion resulting in lack of viral control during chronic infections of the liver. The PD-1 pathway also plays a role in autoimmunity as mice disrupted in this pathway develop autoimmune diseases.
It has been shown that antibodies that block the interaction between PD-1 and PD-L1 enhance T cell responses, in particular the response of CD8+ cytotoxic T cells (see Barber et al 2006 Nature Vol 439 p682 and Maier et al 2007 J. Immunol. Vol 178 p 2714).
WO 2006/042237 describes a method of diagnosing cancer by assessing PD-L1 (B7-H1) expression in tumors and suggests delivering an agent, which interferes with the PD-1/PD-L1 interaction, to a patient. Interfering agents can be antibodies, antibody fragments, siRNA or antisense oligonucleotides. There are no specific examples of such interfering agents nor is there any mentioning of chronic liver infections.
RNA interference mediated inhibition of PD-L1 using double stranded RNA (dsRNA, RNAi or siRNA) molecules have also been disclosed in for example WO 2005/007855, WO 2007/084865 and U.S. Pat. No. 8,507,663. None of these describes targeted delivery to the liver.
Dolina et al. 2013 Molecular Therapy-Nucleic Acids, 2 e72 describes in vivo delivery of PD-L1 targeting siRNA molecules to Kupffer cells thereby enhancing NK and CD8+ T cell clearance in MCMV infected mice. This paper concludes that PD-L1 targeting siRNA molecules delivered to hepatocytes are not effective in relation to enhancing CD8+ T cell effector function.
The siRNA approach is significantly different from the single stranded antisense oligonucleotide approach since the biodistribution and the mode of actions is quite different. As described in Xu et al 2003 Biochem. Biophys. Res. Comm. Vol 306 page 712-717, antisense oligonucleotides and siRNAs have different preferences for target sites in the mRNA.
WO2016/138278 describes inhibition of immune checkpoints including PD-L1, using two or more single stranded antisense oligonucleotides that are linked at their 5′ ends. The application does not mention HBV or targeted delivery to the liver.